Did Mary eventually have sex with Joseph?

According to Church tradition, no.  Mary remained a virgin her entire life.

This belief is reflected in numerous early Church writings.  The Protoevangelium of James, written around A.D. 150, portrays Mary as a consecrated virgin who never had sex with Joseph.  Early Church Fathers, including Augustine and Jerome, spoke of Mary’s perpetual virginity.  Even Martin Luther himself affirmed this teaching.

Admittedly, this tradition is challenging for many modern Catholics.  It’s probably helpful to view it not as a repudiation of marital sexuality, but as a statement of the uniqueness of the Holy Family.  In raising the Son of God, Mary and Joseph had a lot on their plate.   It’s understandable that they would focus on Jesus rather than add additional children to the family.

As the National Conference of Catholic Bishops say in their letter Behold Your Mother: Woman of  Faith,

“God called Mary and Joseph to sublimate the consummation of their married love in exclusive dedication to the holy Child, conceived not by a human father but by the Holy Spirit.”